In an internal combustion engine mounted on a vehicle, it is known that a valve lift amount of an inlet valve and/or an outlet valve are variably controlled in order to improve an output power and/or a fuel consumption. For example, JP-A-2006-144593 teaches a technique for adjusting a valve lift amount by displacing a control shaft as a control axis in an axial direction according to a rotation of a cam. In this case, the cam is rotated and driven by a driving unit such as a motor.
In the above case, in order to maintain the valve lift amount to be a certain amount, it is necessary to keep a rotation angle of the cam within a predetermined angle range. In order to keep the rotation angle of the cam within the predetermined angle range, it is necessary to continue energizing the motor, i.e., to keep flowing current through the motor. In this case, the electric power consumption at a driving circuit for driving the motor increases. Further, when the electric power consumption increases, a running cost and a manufacturing cost of heat radiation system in the electric control device for controlling the driving circuit of the motor and in the driving circuit of the motor. Further, minimizing the dimensions of the electric control device may be difficult.